Photoflash lamp



July 17, 1951 F. G. BROCKMAN PHOTOFLASH LAMP Filed July 26, 1947 FIG!FIG.2

FRANK e. BROCKMAN INVENTOR AGENT types ofalloys.

Patented July 17, 1951 UNITED STATES AT E N-T' OF Fl C-E,

PHOTOFLASH LAMP Frank G. Brockman, DObbSiFBIIX, N:'Y., assignor' toPhilipsLaboratories, l'nc'., Irvington on Hudson, N. Y1

My invention relates to. photoflash lamps of the typewhich employ asolid. combustible material .and more particular to. the combustiblematerial itself. and. to a method of. placing, the same in the lamps.

The majority of. present-day photofiash lamps comprise-a fillingmaterial in the. form of a wire composed of a material which iscombustible with the production of light rays of good actinicproperties. Such. a material is, for; example, aluminum or alloys ofaluminumand magnesium. This wire filling materialmay be. of variouscross-sections, for instance circular or rectangular, and is madeinvarious ways.

In. some'cases, the wireismade. by a drawing processwhereas in. othercases. it ismade by cutting foil into wire of rectangular or squarecrosssections. While the drawing, process produces wire. which givesexceptionally good results, this process is somewhat expensiveWhenusing; some The process of making the wire from foil has thedisadvantage that. it is diiflcult to obtain wire of very smallcross-section. Moreover, the metal or alloy used is restricted tocertaintypes' having, the requisite physical characteristics', for example,ductility.

It is an obj ect of my invention to provide a new and novel photoflashlamp, and a method. of manufacture. thereof.

It is another object of the inventiontoprovide a" filling material whichis economical to manufacture.

Another object ofthe invention is toimprove the manufacture ofphotoflashlamps.

A further object of my invention. is to provide a novel filamentaryfilling materialfor photoflash lamps, and a method of making the same.

A further object of my invention is toprovide a filling material for aphotofiash lamp which may be given a desired predetermined aotinicproperty.

Other objects, advantages, and novel features of the invention. willbecome apparent as the specification progresses;

In accordance with my invention, I provide a photofiash lamp having afilling material of a mixture ofa cementing or plastic material andahigh percentage ofv a finely-divided actinicallyreactive material. Thematerial, according to the invention, may be made by forming the mixtureinto a thin foil, and if desired; then cutting, or shredding wirestherefrom. However, I prefer to extrude the mixture into a filament,preferalbly' of a circular cross-section. The actinicallyreactivematerial may be a mixture of a metallic material and an oxidizing agent;However, Ipre- 2, for to use a metallicmaterial consisting ofafinelydivided metal or mixtures of'metal.

In some. cases, I'prefer to extrude the, wire-at the opening, of thebulb to be filled and carry the wire into the bulb by means; of a streamof gas, as described in the United States. Patent to Cornelis Korver,No. 2,115,423, issued Aprilf26, 1938.

In order that theinvention' may be more clearly understood and readilycarried. into effect, it will now be described with reference to theaccompanying drawing in which:

Figure l is. a cross-sectionalviewof one. form of apparatus for makingaphotoflash lampiin'accordance with the invention; and r Fig. 2 is a.cross-sectional view of aphotoflash lamp in. accordance with theinvention.

As. a. preferred method of production of the combustible fi1ling, aplastic binding material is first put in liquid solution, and a quantityof finely-divided. metal is mixed therewith. The solvent is dried andthe mixture is extruded into filamentary form to produce the filamentfor the lamp. Preferably, I extrude the filament directly into theenvelope of 'thelamp to be manufactured. The following examples willprovide more specific information whereby the invention may bepracticed:

ErampZe1.--One gram of polyethylene is dissolvedin 15 cc. of toluene(CsI-IeCI-Is) to form a viscous solution" at a temperature ofapproximately 100 C. preferably near the boiling" point of toluene. Aquantity of'powdered, atomized, fial ze,v or other finely-dividedaluminum is screened in a 325' mesh screen havinga nominal pore size of.0017 inch and nine grams thereof are homogeneously mixed with thepolyethylenetoluene solution. The toluene is" then evaporated withoccasionalstirring of the mixture to assure uniform dispersion of thecomminuted metal. Whenthe'solventhas been evaporated, I find itconvenient'to compress the resulting mixture into a block suitable touse as a charge in an extrusion press. This charge is then-placed'i'n anextrusion press, suchas the press Iii of Fig. 1, preferably havingheating means such as a heating coil I2 to maintain the temperature ofthe charge at approximately l to l 6G C., whereupon moderate pressure ofthe order of 2,000pounds on piston I 4, which has-a diameter of inch,may be applied 7 and the charge extruded through the'die-apertureresults "are'obtained when theal'uminum constiw -tutesapproximately by"weight of the exwith its extrusion from the die hole i6.

truded mixture. A greater proportion of aluminum, for example over 95%,tends to make the resultant filament brittle. Quantities of aluminumsignificantly less than 90%, for example less than 75%, result in such ahigh oxygen requirement in the finished bulb as to be impractical,partly because the gas in the bulb after reaction will be at appreciablyhigher pressures than before reaction, tending to bulb breakage.

The bulb 18 may be filled by blowing the extruded filamentous materialinto the envelope thereof as described in the aforesaid patent toCornelis, Korver, or the filamentary material maybe separatelycollected, for example on a spool, and thereafter placed in the bulb byany conventional method. In Fig. 1, I have illustrated the formermethod, which I consider preferable, whereby warmed air is blown throughthe jet chambers 20 to carry the extruded filament 2! into the envelopeit) simultaneously This processing has the further advantage that ittends to remove the last remaining traces. of the solvent from theextruded mixture. The usual ignition charge and igniting electrodes arethen inserted in place in the envelope and the bulb sealed.

Example 2.--The filamentous material 2| of the bulb I8 is produced inthe same manner as in Example 1 except that I use as the comminutedmetallic material particles of carbonyl iron of a nominal particle sizeof eight microns (.008 mm.). Again, the best results have been obtainedwith a mixture of about 90% by weight of said iron with respect to thetotal weight of the filament.

Example 3.--One gram of a polyamide, for

, example that commercially sold as Nylon No. FM

101 noted on page 215 in Modern Plastic Encyclopedia, 1946 PlasticsCatalogue, published by Plastics Catalogue Corporation, New York, isdissolved in 20 cc. of normal butyl alcohol at an elevated temperature.About nine grams of comminuted screened aluminum of one of the typesabove mentioned is mixed in the solution in a manner similar to that inwhich the aluminum is mixed in Example 1. The resultant mixture, afterevaporation of the butyl alcohol, is compressed into a slug as a chargefor insertion in the die and then extruded at a temperature of about 210C. A die aperture having a diameter of about .004 inch is also used inthis example, and in other respects, the filling of the bulb 18 may becompleted as before. At the present time, I have achieved the bestresults by utilizing a die pressure near the lowest reasonable flowpressure at slightly elevated temperatures. Thus, in this example, Ifind that the pressure is preferably higher than that utilized inExample 1 when extruding the polyethylene, and that a pressure of about4000 pounds force on the piston M has been found to produce the desiredresults.

Referring now to Fig. 2', there is illustrated a photofiash lamp l8which may be manufactured in accordance with the invention. As aspecific example, a combustible filling 22 of filamentous material isinserted in lamp I8. Material 22 is composed of polyamide and comminutedaluminum dispersed in the polyamide, the aluminum constituting about 90%by weight of the said material. In this example, the bulb l8 enclosesabout '70 cc. of volume, and the filamentous material 22 weighs about 58milligrams. A pulveriz ed igniting mixture 24 of the usual type isinserted in the lamp and electrodes 26 leading thereto are sealed at 28into the base of the tube. When the mixture 2 3 is flashed byapplication of a suitable potential to the electrodes 26, sufficientconcentrated energy is produced to start the reaction of adjacentparticles of the combustible filling material with the oxygen in theenvelope. As the reaction progresses, the binder or plastic of thefilling material is volatilized by the energy released and theactinically-reactive metallic material is freed to react with theoxygen. It is probable that the plastic simultaneously reacts to produceactinic radiation. In any event, I obtain a flash lamp of good actinicproperties.

The filaments produced by the foregoing methods have a diameterapproximating the diameter of the aperture of the die, and in the aboveexamples, the maximum diameter is about .006 inch. The binders for themetal powder, as above described, have generally the property of formingstrong fibers by themselves. This property may be attributed to the factthat the molecules of the fibers or filaments may be oriented lengthwisethereof to provide comparatively high tensile strength and I have foundthat the use of such binders is preferable in order to produce afilament having a high ratio of metal to binder. Furthermore, I havefound it preferable, as noted above, to insert the filamentous materialimmediately after its extrusion into the envelope of the lamp whereby agreater uniformity of distribution of the filament in the envelope isachieved, and deleterious changes of the properties of the filament areavoided. Another advantage of placing the filament directly into theenvelope is that such changes in the flexibility of the material withtime, as may occur, take place after the material has assumed its finalposition in the envelope and, therefore, breakage of the filament due tobrittleness is avoided and proper distribution of the filament in theenvelope is facilitated.

It will be apparent that by choosing the metallic particles suitably, orby suitable mixtures thereof, the actinic radiation of the lamp may becontrolled to a degree not hitherto possible without great practicaldifficulties.

Thus, many desirable materials which cannot be drawn to small diametersor made into thin foils may be utilized in the filamentous material ofthe invention.

One may also use as the actinically-reactive substance mixed in theplastic a mixture of a metal or metals and an oxidizing agent. Forexample, a mixture of aluminum and sodium chlorate by about by weight ismixed with a suitable plastic, for example, one of those notedhereinbefore, by about 10% by weight. The proportion of plastic may beincreased, particularly if enough excess of oxidizing agent is includedto oxidize the plastic material, and the bulb may then be completelyevacuated.

In those instances where the filament upon extrusion is wound on aspool, it is preferable to apply a slight tension to the emergingfilament during its extrusion to assist in the fiow of material throughthe die aperture.

Instead of extruding the filament in a hot state as described above, itis possible to extrude the filament in a cold state by controlling theprior evaporation of the solvent from the mixture of plastic, solvent,and :actinically-reactive particles, so that the solution i of theproper plasticity to be extruded through the die aperture. The metallicparticles may be mixed in the plastic material by heating the plasticmaterial to a liquid state, and thereafter mixing the metallic particlesinto the liquid, no solvent being used.

While I have described my invention with specific examples, and in aspecific embodiment, I do not wish to be limited thereto since obviousmodifications will suggest themselves to those skilled in the artwithout departing from the scope and spirit of the invention.

What I claim is:

1. A photofiash lamp comprising an envelope having an actinic lighttransmitting portion and a filamentous material distributed within saidenvelope, said filamentous material comprising a plastic bindingmaterial and a major proportion of finely-divided actinically-reactivemetallic particles dispersed in said plastic, said filamentous materialhaving a diameter of less than about .006 inch, said particles having aparticle size of less than about .002 inch.

2. A combustible filling material for a photoflash lamp comprising afilament of polyethylene and a comminuted actinically-reactive metallicmaterial dispersed in said polyethylene, said filament consistin ofabout by weight of polyethylene and about 90% by weight of said metallicmaterial.

3. A combustible filling material for a photofiash lamp comprising afilament of polyamide and comminuted metallic material dispersed in saidpolyamide, said filament consisting of about 10% by weight of polyamideand about 90% by weight of said metallic material.

4. In the manufacture of a photoflash lamp, the method of producing anactinically-reactive filament for insertion in said lamp, comprising thesteps of dissolving a plastic and a solvent, mixing in said solutionfinely comminuted metallic material in the ratio of about three parts toabout nineteen parts by weight of metallic material to about one part byWeight of plastic, evaporating the solvent from said mixture, andextruding the mixture in fine diameter into a filament of substantiallength for insertion in said lamp.

5. In the manufacture of a photofiash lamp, the method of producing anactinically-reactive filament for insertion in said lamp, comprising thesteps of dissolving polyethylene in toluene, mixing a finely-dividedmetallic material in said solution, evaporating the toluene from saidmixture, and extruding the mixture in fine diameter into a filament ofsubstantial length for insertion in said lamp.

6. In the manufacture of a photofiash lamp, the method of producing anactinically-reactive filament for insertion in said lamp, comprising thesteps of dissolving a polyamide in normal butyl alcohol, mixing afinely-divided metallic material in said solution, evaporating thenormal butyl alcohol from said mixture, and extruding the mixture infine diameter into a filament of substantial length for insertion insaid lamp.

FRANK G. BROCKMAN.

REFERENCES CITED The following references are of record in the v file ofthis patent:

UNITED STATES PATENTS Number Name Date 594,594 Bostwick Nov. 30, 1897613,021 Schwartz Oct. 25, 1898 2,115,423 Korver Apr. 26, 1938 2,149,694Vollrath Mar. 7, 1939 2,158,415 Formhals May 16, 1939 2,205,081 Burrowset al June 18, 1940 2,272,779 Sarbey Feb. 10, 1942 2,363,569 Caldwell eta1. Nov. 28, 1944

